Polyfluoroaromatic nitriles

ABSTRACT

The difunctional polyfluoroaromatic compounds represented by the formula ##STR1## wherein X and Y are identical and are selected from the class consisting of --COOR 1 , --CH 2  NH 2 , --CH 2  NCO and ##STR2## wherein R 1  is --H, alkyl and R 2  and R 3  independently are either --H, X or alkyl and n is either 0 or 1 are disclosed. These compounds are derived from those wherein X and Y are --CN which are produced in a solvent specific reaction. The process comprises reacting pentafluorobenzonitrile with a Grignard reagent of the formula CH 3  MgHal, wherein Hal is --Cl or --Br, in the presence of either tetrahydrofuran, 1,3-dioxolane, dimethoxyethane or diglyme. When the solvent employed is tetrahydrofuran, the cyano compound wherein n is 1 is obtained. When the solvent is 1,3-dioxolane, the cyano compound wherein n is 0 is obtained.

BACKGROUND OF THE INVENTION

The prior art has long recognized the versatility of perfluoroaromaticmonomers in the production of polymers having high thermal stability.U.S. Pat. Nos. 3,694,495; 3,629,340 and 3,394,190 are exemplary of theuse of such compounds as polymeric intermediates.

Further, such compounds have been emploed as intermediates in theproduction of pyrethroid insecticides. For example, U.S. Pat. Nos.4,385,070 and 4,486,355 disclose compounds of the formula ##STR3##wherein R is nitro, cyano, lower alkoxycarbonyl, lower alkylcarbonyl, ordi- or trifluoromethyl which are used as intermediates in the productionof benzyl esters having insecticidal and acaricidal activity. Thecompound wherein R is --CN may be prepared by carboxylation of thecorresponding methyltetrafluorobenzene and subsequent derivativizationof the carboxylic acid group, as set forth below: ##STR4## Since thisreaction sequence and similar reaction sequences for producing suchdifunctional compounds are not particularly cost effective, alternativemethods for the production of the difunctional intermediates arecontinuously being advanced.

A simplified method of producing para-substituted difunctionalderivatives of pentafluorobenzonitrile would be by a Grignard synthesis.

However, the prior art teaches that the reaction of a Grignard reagentand a pentafluoroaromatic compound substituted with such electronwithdrawing groups as --CN, --COR and --COOR, wherein R is an alkylgroup, will not produce the desired para substituted compounds.

For example, Birchall et al in an early study illustrated that thereaction of pentafluorobenzonitrile (PFBN), represented by the formula##STR5## with phenylmagnesium bromide in ether renderedpentafluorobenzophenone via the intermediate imine hydrochloride, C₆ F₅CPh:N⁺ H₂ Cl. (J. Chem. Soc. (C), 1971, 7, 1343).

Further, studies by T. N. Gerasimova show that when the startingreactants contain a --COOR group versus a --CN, the ortho substitutedproduct is obtained, as represented by the following reactionmechanisms: ##STR6## where R=--CH₃ or --CH(CH₃)₂ ; and R¹ =C₁ -C₄ alkylor phenyl. Izv. Sib. Otd. Akad. Nauk SSSR, Ser. Khim. Nauk 1975, (5),100-6.

SUMMARY OF THE INVENTION

The present invention is drawn to a process for preparingcyano-containing difunctional derivatives of pentafluorobenzonitrile,compounds produced therefrom and derivatives of such compounds. Thecompounds of this invention are extremely useful as intermediates in thesynthesis of either cyclopropane carboxylates or high temperature stablepolymers.

DETAILED DESCRIPTION OF THE INVENTION

The compounds of this invention may be represented by the formula:##STR7## wherein X and Y for any given compound are identicalsubstituent groups and are selected from the class consisting of

--CN

--COOR¹

--CH₂ NH₂

--CH₂ NCO; or ##STR8## wherein for any given compound (i) R¹ may beeither hydrogen or an alkyl group;

(ii) R² and R³, independent of one another, are either hydrogen, halogenor alkyl: and

(iii) n is either 0 or 1.

The alkyl group for R¹ preferably contains 1 to 6 carbon atoms and forR² and R³ preferably contains 1 to 4 carbon atoms. Further, the halogenatom for R² and R³ is preferably a chlorine, bromine or fluorine atom.Thus, while R¹, R² and R³ are independent of one another, each of R¹, R²and R³ are represented by one substituent for any given compound.Likewise, X and Y are both represented by only one of the aforementionedsubstituents for any given compound.

While useful as intermediates in the production of insecticides and hightemperature stable polymers, it was further found that these compoundsmay increase cohesive strength and tackiness in synthetic rubbercompositions.

The compounds wherein X and Y are both --CN are the precursors for theother compounds of this invention. These compounds may be produced ingood yields by a Grignard synthesis. In particular, these compounds areproduced by reacting pentafluorobenzonitrile (PFBN) and a Grignardreagent of the formula CH₃ MgHal, wherein Hal is either chlorine orbromine, in a reaction medium. The principal products obtained are ofthe formula: ##STR9##

The selection of the solvent is critical, however, upon the yieldobtained and the resulting product. The solvents demonstrating adramatic effect on the product distribution are:

1. 1,3-Dioxolane. It was discovered that use of the solvent1,3-dioxolane renders the substitution of the --CH₂ CN group for thefluorine group of PFBN. The resulting compound,4-cyano-2,3,5,6-tetrafluorobenzyl cyanide, represented by formula(XVIII) wherein Y is --CN and n is 0, is especially useful as anintermediate in the production of specialty polymers. Further, byemploying 1,3-dioxolane as solvent, only small amounts of3-methyl-4-cyano-2,5,6-trifluorobenzyl cyanide,2,3,5,6-tetrafluoro-p-toluonitrile and4-acetyl-1,2,3,5,6-pentafluorobenzene by-products are obtained.

2. Tetrahydrofuran. When the reaction is conducted in the presence oftetrahydrofuran (THF), the principal product obtained is 4,4'-methylenebis(tetrafluorobenzonitrile) (bis TFBN); as represented by formula(XVIII) above wherein Y is --CN and n is 1. This compound is likewisesuitable as an intermediate in the production of polyesters andpolyamides.

3. Dimethoxyethane and Diglyme. It was further discovered that when thereaction is conducted in the presence of either dimethoxyethane (DME) ordiglyme, the principal product obtained is2,3,5,6-tetrafluoro-p-toluonitrile (TFTN). This product may further berepresented by formula (XVIII) wherein n is 0 and Y is H. This compoundmay be employed as an intermediate in the synthesis of pesticidalcompounds as disclosed in U.K. patent application No. 2,135,306A.Especially desirous results are obtained when the solvent employed isDME. It is most preferable to use redistilled DME or DME treated withmolecular sieves (Aldrich 13x, 8 mesh) in order to avoid any sidereactions involving peroxide impurities.

Thus, the reaction of PFBN and the Grignard reagent is solvent specific;TFTN being the major product when the solvent is either DME or diglyme;bis TFBN being the major product when the solvent is THF; and4-cyano-2,3,5,6-tetrafluorobenzyl cyanide being the major product whenthe solvent is 1,3-dioxolane.

The PFBN and Grignard reagent are generally reacted between 0.25 and 4hours, preferably between 1 and 2 hours, between -20° C. and 35° C. Thepreferred temperature range is 10°-25° C. Generally, the desiredreaction will proceed more slowly at the lower end of the temperaturerange than at the higher end. For example, when tetrahydrofuran isemployed as solvent, the reaction may be completed in 10 minutes at 10°C. with a moderate excess of Grignard reactant being employed versus inseveral hours at -20° C. with a lower excess of Grignard being employed.The reaction is terminated by the addition of either 0.5N to 6N,preferably 4N, acid solution, preferably HCl or NH₄ Cl or water.

The molar ratio of Grignard reagent to PFBN is between 1.0 and 3.0, mostpreferably between 1.2 and 1.6. Generally at the lower end of this scalethe reaction may be incomplete whereas the formation of bis TFBN andhigher condensation products are favored at the higher end.

The PFBN is generally dissolved in the solvent media prior to admixingthe Grignard reagent. The amount of PFBN to solvent is from 1:3 to 1:30(weight/volume), preferably between 1:6 to 1:15, most preferably 1:10.Further, the Grignard reagent is preferably dissolved in an organicsolvent, such as tetrahydrofuran (THF) and diethyl ether, mostpreferably tetrahydrofuran, prior to admixing it with the PFBN solution.The concentration of Grignard reagent in the organic solvent ispreferably between 2.0 and 3.5 molar.

In the Grignard reagent, Hal is either --Cl or --Br. Since the use ofCH₃ MgBr leads to greater by-product formation, particularly,3-methyl-4-cyano-2,5,6-trifluorobenzyl cyanide, the Grignard reagentpreferably contains a chlorine atom for the X substituent, when thesolvent is 1,3-dioxolane.

The reactant pentafluorobenzonitrile (PFBN) may be commerciallyobtained. Alternatively, it may be obtained by fluorinating thecommercial product pentachlorobenzonitrile with potassium fluoride in apolar aprotic solvent.

The compounds of formula (XVII) wherein X and Y are --CN are especiallyuseful as intermediates in the production of high stable polyesters andpolyamides since the cyano groups can easily be hydrolyzed orhydrogenated, respectively. For example, the compound can becatalytically hydrogenated according to the reaction ##STR10## Further,the compound could be hydrolyzed by dilute acid according to thereaction ##STR11##

The corresponding diisocyanate and N N'-bis-maleimide can further beprepared from the reduced product and subsequently employed in theproduction of polyurethanes and thermoplastic polymeric products,respectively. For example, such compounds can be prepared by reactingthe diamine with an acid anhydride, such as maleic anhydride, and thenreacting the resulting maleamic acid with acetic anhydride and an alkaliacetate to yield the desired N,N'-bis-maleimide. This reaction may besummarized as: ##STR12##

The examples which follow are presented to illustrate the invention andthe advantages thereof. They are not, however, intended to limit thescope of the invention.

EXAMPLE 1

A 2.8 molar solution of methyl magnesium chloride in 115 ml. oftetrahydrofuran (THF) was added dropwise to a stirred solution of 30.9g. of pentafluorobenzonitrile in 300 ml. of tetrahydrofuran undernitrogen between -15° to -20° C. The addition was complete in 28minutes. The reaction product was then stirred for 1 hour at -15° C. Tothis solution was slowly added, 150 ml. THF/H₂ O (1:1 v/v), followed by150 ml. of 4N HCl solution. The product was stirred at room temperatureuntil all solids were dissolved. The uppermost product layer wasseparated and evaporated to a small volume, then dissolved in 175 ml. ofmethylene chloride. This methylene chloride solution was then washedwith 25 ml. of water four times followed by 25 ml. solution of 5% sodiumbicarbonate and 25 ml. of water. The methylene chloride solution wasthen vacuum stripped at 45° C./25 mm to render 27.2 grams of product.Analysis by gas liquid chromatography indicated that 40% of this productwas bis TFBN, and 20% TFTN. This product was left to crystallize at roomtemperature for approximately 24 hours and, after filtration, andremoving the filtrate a light yellow solid identified as 4,4' -methylenebis(2,3,5,6-tetrafluorobenzonitrile) (bis TFBN), and having a meltingpoint between 112°-115° C. after washing with methanol, was obtained.Recrystallization from 5 parts of methanol gave pure 4,4'-methylenebis(2,3,5, 6-tetrafluorobenzonitrile) (bis TFBN), with a melting pointbetween 114°-116° C. The compound had the following chemical analysis:C, 49.78%; H, 0.62%: F, 39.42%; and N, 7.86%. Calc: C, 49.75%; H, 0.56%;F, 41.98%; and N, 7.73%. 4,4'-Methylenebis(2,3,5,6-tetrafluorobenzonitrile) (bis TFBN) was identified by NMRand GC/MS. The filtrate was then fractionally distilled in a Vigreuxcolumn under high vacuum at 170° C./8mm. 5.8 grams of a colorless liquiddistilling at 72°-75° C./8 mm Hg. was obtained. This compound wasidentified by NMR and GC/MS as 2,3,5,6-tetrafluoro-p-toluonitrile(TFTN). The distillation residue, not distillable below a pottemperature of 170° C./8 mm was crystallized on standing at roomtemperature. This product weighing 14.0 grams was identified by NMR andGC/MS as being predominately 4,4'-methylenebis-(2,3,5,6-tetrafluorobenzonitrile) (bis TFBN) and may be furtherpurified by recrystallization from methanol at 0° C.

EXAMPLE 2

Pentafluorobenzonitrile (17.8 g.) was dissolved in 178 ml. of1,3-dioxolane. The resulting solution was cooled to 20° C. The solutionwas stirred under nitrogen while adding 48 ml. of methyl magnesiumchloride solution in tetrahydrofuran (2.8M) dropwise during a period of35 minutes while the temperature was maintained at 20° C. withoccasional cooling. Stirring was then continued at 20° C. for one hour.To the resulting solution was gradually added 38.4 ml. of 4N HCl at15°-22° C. and 154 ml. of methylene chloride. The mixture was thenstirred and allowed to separate. The lower acidic phase was discardedand the organic layer was washed five times with a mixture of 56 ml. ofwater and 20 ml. of brine (a 10% by wt. sodium chloride solutionobtained by mixing 100 g of sodium chloride in 1 liter of water) untilthe pH was 3.5. 16.1 g. of crude product was then isolated by strippingin vacuum. The crude product was then purified by distilling at aboiling point between 122°-128° C./1 mm. The yield was about 65%. Theproduct was further purified by treating it with a small amount ofmethanol, approximately 4 g. of product to 1 ml. of methanol, andcrystallizing the resulting product at 0° C. The purified product wasthen isolated by filtration. The melting point of the product wasbetween 48°-52° C. Analysis by gas liquid chromatography indicated theproduct was 85-90% pure. The compound was identified by massspectrometry and NMR to be 4-cyano-2,3,5,6-tetrafluorobenzyl cyanide.

Analysis: C, 49.79%; H, 1.09%; N, 12.12% Calc: C, 50.48%; H, 0.94%; N,13.08%

EXAMPLE 3

PFBN (32.6 g) was dissolved in 325 ml of DME. A 2.8 molar solution ofmethyl magnesium chloride in THF (85 ml) was then added to the stirredPFBN solution dropwise under N₂ at 0°-5° C. in 1 hr. The reaction wascontinued for 11/2 hours at 0°-5° C. and was then terminated by adding4N HCl (74 ml) slowly at 5° C. The product consisted of two layers.After addition of 275 ml methylene chloride, the aqueous layer wasseparated and discarded. The product solution was washed once with 150ml H₂ O and three times with brine. The solvents were distilled off at40°-60° C. under slight to moderate vacuum and TFTN was then recoveredfrom the solvent-free product by distillation at 65°-70° C./6 mm andidentified by NMR and GC/MS analysis. The yield of high purity TFTN was11.3 g.

EXAMPLES 4-5

The experimental procedure of Examples 2 and was repeated under theconditions indicated below. GC analysis demonstrated the productdistribution as indicated.

    ______________________________________                                               Molar Ratio                                                                   of CH.sub.3 MgCl/                                                                        Reaction     Reaction                                       Example                                                                              PFBN       Temperature  Time   Solvent                                 ______________________________________                                        4      1.125      -15° to -20° C.                                                                1 hr.                                                                              THF                                     5      1.185      25° C.                                                                              0.5 hr.                                                                              THF                                     ______________________________________                                        GC Analysis (Product Ratios)                                                         PFBN          TFTN    bis TFBN                                         ______________________________________                                        4      25            22      36                                               5       1            13.8    26.9                                             ______________________________________                                    

EXAMPLE 6

Pentafluorobenzonitrile (1 g.) was dissolved in 10 ml. ofdimethoxyethane. The solution was stirred at room temperature. 2.5 ml ofa 2.8 molar solution of methyl magnesium chloride in tetrahydrofuran wasadded slowly to the solution while the temperature was maintained at 25°C. through occasional cooling. After a reaction period of approximately30 minutes, 2 ml of 4N HCl and 8 ml. of methylene chloride was added.The methylene chloride solution was separated and washed four times with3 ml. of water or 3 ml. of an aqueous brine solution. Diphenyl ether(0.25 g.) was added to the reaction in order to facilitate GC analysis.The GC analysis indicated that a product ratio of 29:20 of2,3,5,6-tetrafluoro-p-toluonitrile (TFTN) and 4,4'-methylenebis(2,3,5,6-tetrafluorobenzonitrile) (bis TFBN) was obtained.

EXAMPLES 7-12

The experimental procedure of Example 6 was repeated employing thefollowing parameters:

    ______________________________________                                               Molar      Amount of                                                          Ratio of   2.8 Molar                                                          CH.sub.3 MgCl/                                                                           CH.sub.3 MgCl                                                                            Reaction Reaction                                Example                                                                              PFBN       added (ml) Temperature                                                                            Time                                    ______________________________________                                         7     1.10       2.1        25° C.                                                                          0.5 hr.                                  8     1.20       2.2        25° C.                                                                          0.5 hr.                                  9     1.26       2.3        25° C.                                                                          0.5 hr.                                 10     1.29       2.4         0° C.                                                                          1.0 hr.                                 11     1.40       2.6         0° C.                                                                          0.5 hr.                                 12     1.51       2.8        -10° C.                                                                         2.0 hr.                                 ______________________________________                                    

GLC Analysis rendered the following product distribution (ratio).

    ______________________________________                                        PFBN             TFTN    bis TFBN                                             ______________________________________                                        7       40           25      11                                               8       11           26      8                                                9       15           24      6.5                                              10      11.2         30      18                                               11      5.2          32      21                                               12      14           28      18                                               ______________________________________                                    

The yield of 2,3,5,6-tetrafluoro-p-toluonitrile (TFTN) in Example 10measured by GLC against diphenylether, the internal standard, wasapproximately 44% with 17% pentafluorobenzonitrile being unreacted. Theyield of 4,4'-methylene bis(2,3,5,6-tetrafluorobenzonitrile (bis TFBN)was 22%. The examples illustrate the reversal of2,3,5,6-tetrafluoro-p-toluonitrile (TFTN): 4,4'-methylenebis(2,3,5,6-tetrafluorobenzonitrile (bis TFBN) ratio in the productswhen dimethoxyethane is used as solvent instead of tetrahydrofuran.

EXAMPLE 13

To a one liter round bottom flask is added 100 g of the compound ofExample 2 and 300 ml of an 18N sulfuric acid solution. The solution isheated for 4 hours at 130°-150° C. The resulting acid is isolated byadding the resulting crude product solution to 1 liter ice water andfiltration. The product is then washed with water and dried.

EXAMPLE 14

To a one liter round bottom flask is added 100 g of the compound ofExample 1 and 300 ml of an 18N sulfuric acid solution. The solution isheated for 6 hours at 150°-170° C. The resulting acid is isolated byadding to 1 liter ice water and filtration. The product is washed withwater and dried.

EXAMPLE 15

Into a 300 ml autoclave is added 10 g of the compound of Example 1, bisTFBN, 22 ml of isopropanol, 26 ml of water, 7.2 g of concentratedsulfuric acid and 1.5 g of 5% Pd/C. After flushing with nitrogen, 880psi of hydrogen pressure is applied and stirring at room temperature iscontinued for 5.5 hours. The reaction mixture is filtered and carefullywashed with aqueous isopropanol. Isopropanol is then removed bydistillation and an aqueous sodium hydroxide solution is slowly added tothe residue until the pH is basic. The product is then dissolved inether and dried with Na₂ SO₄. After evaporation of the solvent, theproduct obtained is a white solid.

EXAMPLE 16

7 Parts of chlorobenzene are stirred and cooled to -7° C. in a reactionvessel. 2 Parts of phosgene is then introduced into the reaction vessel.1.5 Parts of the reaction product of Example 15, 4,4'-methylenebis(2,3,5,6-tetrafluoro)benzylamine, are gradually added to the solutionand stirring is then continued at a temperature which ranges between 25°and 40° C. while additional phosgene is slowly introduced. After themild exothermic reaction has subsided, the solution is stirred for 2hours at a temperature between 60° and 80° C. Negligible residual HClevolution occurs at the end of the reaction. The product solution isthen sparged with nitrogen, filtered and stripped in vacuum until aviscous syrup is obtained. The diisocyanate product may be purified byextraction with hexane.

EXAMPLE 17

3.3 Mol of maleic anhydride is dissolved in 350 ml of acetone, and thesolution obtained is introduced into a 2-liter reactor provided with astirrer and a thermometer. The reactor is further placed in a coolingbath consisting of a mixture of water and ice. 1.5 Mol of the compoundof Example 15 in solution in 800 ml of solvent consisting of a mixtureof dimethyl formamide and chloroform in equal volumes is slowlyintroduced into the reactor with vigorous stirring. The rate of flow isso adjusted that the temperature of the reaction mass remains below 20°C. The bis-maleamic acid compound precipitates as it is formed and isrecovered by filtration at the end of the reaction. The product iswashed with acetone and dried. 0.5 Mol of the bis-maleamic acid is thenintroduced into a reactor which is provided with a thermometer, acentral stirring system, and can be heated by a water bath. Thefollowing ingredients are introduced into the reactor:

1.5 mol of acetic anhydride,

300 ml of dimethyl formamide,

10 g of sodium acetate.

The temperature is gently raised to 60° C., and the reaction mass ismaintained at this temperature for 1 hour. After cooling to 15° C., theexcess of anhydride is destroyed by adding a little water, and thebisimide crystallizes out. After filtration, the product is washed withwater and dried.

Preparation A: Synthesis of a Polyester with a Final Acid Value ofAppoximately 25 and a Low Softening Point.

0.2 Mol of ethylene glycol and 0.2 mol of neopentyl glycol areintroduced into a 250 ml round bottom flask, fitted for stirring,heating, distillation, addition of reactants and maintenance of an inertgas atmosphere. After sweeping the flask with nitrogen, slow stirringand heating are begun and 0.02 grams of a technical grade ofhydroquinone (polymerization inhibitor) is added. Thereafter slowaddition of 50 grams of the acid of Preparation A is begun anddistillation starts at 150°-170° C. After reaching cooking temperature(210° C.), 20 g maleic anhydride is added and the mixture is heatedunder nitrogen with stirring for 8 hours. Vacuum is applied to thesystem for 30 minutes before the end of the cook. The resin is thenpoured into a flat aluminum tray to cool, harden and subsequently brokenup and ground. The final acid value of the resinous product isapproximately 25 and has a low softening point.

Preparation B: Synthesis of a Polyester with a Moderately High SofteningPoint.

0.2 Mol of ethylene glycol and 0.2 mol of neopentyl glycol areintroduced into a 250 ml round bottom flask, fitted for stirring,heating, distillation, addition of reactants and maintenance of an inertgas atmosphere. After sweeping the flask with nitrogen, slow stirringand heating are begun and 0.02 grams of a technical grade ofhydroquinone (polymerization inhibitor) is added. Thereafter slowaddition of 80 grams of the acid of Preparation B is begun anddistillation starts at 150°-170° C. After reaching cooking temperature(210° C.), 20 g maleic anhydride is added and the mixture is heatedunder nitrogen with stirring for 8 hours. Vacuum is applied to thesystem for 30 minutes before the end of the cook. The resin is thenpoured into a flat aluminum tray to cool, harden and subsequently brokenup and ground. The final acid value of the resinous product isapproximately 25 and has a moderately high softening point.

Preparation C: Synthesis of a Synthetic Rubber Composition HavingIncreased Cohesive Strength and Tackiness.

100 parts by weight (pbw) of polyisoprene, 1.5 pbw of low molecularweight butadiene rubber containing 5% of nitrosodiphenylamine groups,0.1 pbw of the acid of Preparation A, 0.5 pbw of sulphur, 0.4 pbw ofdibenzylthiazolyl disulphide, 1.0 pbw of diphenyl guanidine, 1.0 pbw ofstearic acid, 2.0 pbw of zinc oxide and 20 pbw of technical carbon wasmilled and then vulcanized for 20 minutes at 406K. The cohesion andtackiness of the resulting composition was equal to that of naturalrubber.

What is claimed is:
 1. The compound of the formula ##STR13##
 2. Thecompound of the formula: ##STR14##